Human cytomegalovirus is the most common cause of congenital infection leading to mental retardation, deafness, and other neurological handicaps in the United States. Moreover, immunocompromised patients, such as those with cancer, acquired immunodeficiency syndrome (AIDS) and organ transplant recipients are at high risk for developing HCMV infection. M. Ho, Cytomegalovirus Biology and Infection, Plenum Publishing Corp., New York, 1-275 (1982); F. Rapp, Comprehensive Virology, 16, 193-232 (1980).
HCMV is a member of the family herpesviridae. HCMV virions consist of a linear double-stranded DNA molecule enclosed within an icosahedral nucleocapsid, surrounded by a tegument and a lipid-containing envelope containing a number of viral glycoproteins and glycoprotein complexes. Several distinct viral glycoproteins have been identified in the envelope of HCMV by the utilization of monoclonal antibody technology to immunoprecipitate the glycoproteins. See, for example, D. Gretch et al., J. Virol., 62, 875-881 (1988). Some of these glycoproteins are in disulfide-linked complexes that can be separated by rate zonal centrifugation. Gretch et al. have identified three glycoprotein complexes (gc) designated as gcI, gcII, and gcIII.
The major component of the outer HCMV virion envelope is the glycoprotein complex gcI, which contains a homolog of herpes simplex virus (HSV) glycoprotein B (gB). The complex gcI consists of a 55 kilodalton (kDa) glycoprotein, designated as gp55, in a disulfide-linked complex with a heterogeneous glycoprotein designated as gp93-130. W. Britt et al., J. Virol., 63, 403-410 (1989); D. Gretch et al., J. Gen. Virol., 69, 1205-1215 (1988). The gene encoding gp55 has been identified, and maps between 0.344 and 0.360 map units (m.u.). This gene exhibits extensive homology with the glycoprotein B gene of herpes simplex virus (HSV) type 1. M. Cranage et al., EMBO J., 5, 3057-3063 (1986); M. Mach et al., J. Gen. Virol., 67, 1461-1467 (1986).
A second set of antigenically related complexes, designated gcII, appears to represent multimeric forms of one or more gene products. The isolation and characterization of the principal glycoprotein contained within this family of complexes, gp47-52, has been described in detail in co-pending U.S. patent application Ser. No. 06/933,789, filed Nov. 24, 1986, wherein it is referred to as GLP-B, and in co-pending U.S. patent application Ser. No. 07/158,389, filed Feb. 22, 1988, wherein it is referred to as gp52(II).
K. Weston et al., J. Mol. Biol., 192, 177-208 (1986), have sequenced the short unique (U.sub.s) region of the HCMV genome (AD169 strain), revealing at least 38 open reading frames (ORFs) that potentially code for (glyco)proteins of HCMV. One gene family, designated HXLF (HindIII X left reading frame), consists of five ORFs that lie in tandem with varying degrees of homology. The HXLF1 and HXLF2 genes code for proteins of 21 to 25 kDa and 20 kDa, respectively, which are glycosylated to glycoproteins of 47 to 52 kDa (gp47-52). D. Gretch et al., J Virol., 62, 875-881 (1988).
Glycoproteins with molecular weights of 86 kDa and 145 kDa have been isolated from a third HCMV glycoprotein complex, designated as gcIII. gp86 is a homolog of HSV gH. The gene encoding gp86 has been identified, and maps between 0.45 and 0.47 m.u. M. Cranage et al., J. Virol., 62, 1416-1422 (1988). The gene which encodes gp145 has not been identified, however.
Gene expression of the human cytomegalovirus can be broadly categorized in three functional phases, immediate-early (IE), early, and late. The genes relating to these phases are transcribed in sequential order beginning with the restricted transcription of IE genes. These IE genes are in a large, unique genome segment that encodes for the regulatory proteins required for the subsequent expression of early genes involved in DNA replication and late genes encoding for structural proteins and glycoproteins in mature virions. This genome segment is the U.sub.L region. In particular, this region includes three IE genes and a promotor-regulatory segment (the IE transcriptional regulatory unit) that controls the temporal expression of all the genes of the HCMV genome. Each IE gene encodes one or more mRNA transcripts which code for the regulatory proteins.
The mechanisms that regulate expression of viral early and late genes and the functions of their products are important to the replication of HCMV. The early genes are expressed but their products are unknown at present. Therefore, it is an object of the present invention to identify the early viral envelope glycoproteins of HCMV and their polypeptide precursors, and to identify and characterize the genes encoding these proteins, a further object is to determine the immunogenicity of these proteins and develop antibodies and vaccines against them.